Conventionally, there has been known a vibration-damping device, as a type of vibration-damping device to be interposed between members constituting a vibration transmission system, having a first mounting member and a second mounting member connected by a main rubber elastic body. Engine mounts, body mounts, suspension supports or vibration damping bushes for motor vehicles, for example, are such devices.
In such a vibration-damping device, a stopper mechanism is adopted to restrict relative displacement between the first mounting member and the second mounting member for the purpose of limiting the amount of elastic deformation of the main rubber elastic body and relative displacement between the members at an excessive load input. Such a stopper mechanism is generally configured by providing first and second stopper portions arranged face to face in the direction of relative displacement between the first and second mounting members so as to abut against each other via a rubber buffer layer.
Meanwhile, the stopper mechanism is required to have a buffer function to alleviate the shock at the time of contact between the first and second stopper portions as well as a displacement limiting function that reliably controls relative displacement between the first and second stopper portions. As to the former, it is effective to make the rubber buffer with a larger volume to let it exert soft spring characteristics. So, it has conventionally been treated by thickening the rubber buffer layer, providing concaves and convexes, and setting the rubber hardness low enough.
However, such a treatment had a problem of lowering the reliability of the displacement limiting function of the latter, making it difficult to get both functions at the same time. In addition, since the size of the space that can be set between the opposing faces of the first and second stopper portions where the rubber buffer is arranged is limited by the relation with other members and the like, it was sometimes difficult by itself to set enough thickness for the rubber buffer layer.
In order to deal with this kind of problem, the present applicant previously proposed a structure where the thickness dimension of the rubber buffer layer is made larger by providing a concave recess at a position facing the stopper portion in Japanese Unexamined Patent Publication No. JP-A-2005-106138 (Patent Document 1). However, although such a structure is effective in setting the thickness dimension of the rubber buffer layer substantially large enough while maintaining the durability thereof, if the rubber buffer layer has a Poisson ratio of about 1/2, its lowered spring constant requires an improvement in the buffer function in some cases.